Wow, the Homeworld galaxy is M 51? I should note that SE does not directly support placing stars in other galaxies, their particles may jump on screen when you try to approach them. However, inside the planetary system there should be no round errors.

I have a 3d model of exterior/interior spaceship, with corridors and lot of things

That would probably not be the best thing to put in SE alongside this model because the size of the model and the number of textures (mostly the latter) would probably crash the program. I've been helping him test that model in SE and already the textures had to be massively downsized to avoid crashing. Adding an interior would likely more than double the number of textures in use and SE probably could not handle that much memory being used at once.

The ship is a render model as are the shuttles for it. I had to reduce the poly count and the textures were all 2048x2048 which is far too much so I reduced those to 512x512. Its a lot of textures but the model over all works in SE. I may make 3 versions of Serenity, one without shuttles, one with a single shuttle, and one with 2 shuttles.